The first cigarette filters were developed in the 1920s and were composed of crepe paper, sometimes together with cellulose wadding. Subsequent concerns over the adverse link between smoking and health led to a surge in demand for filters yielding lower tar levels. A dual filter comprising cellulose acetate fibres within a paper sheath was developed, allowing for the addition of other functional components such as activated carbon.
Further concerns over health, increased legislation and market pressures for reduced tar, nicotine and carbon monoxide levels require continued development in filter technology. Today the global market for cigarettes exceeds 5.8 trillion sticks per annum, 97% of which now contain filters. Of the filtered cigarettes 80.4% are made from standard cellulose acetate fibre (4.5 trillion sticks), 16.6% are classed as ‘special’ filters and 3% are made from polypropylene.
Typically cigarette filters comprise a “filter tow,” generally crimped fibres of cellulose acetate, encased in a tipping paper. This invention is concerned with the filter tow component.
One of the most pressing issues for manufacturers of cigarettes and cigarette filters is the rate at which the filters biodegrade. Cellulose acetate filters can take between one month and three years to biodegrade, dependant on environmental conditions, which is not sufficiently fast to avoid the issue of litter. Discarded cigarette filters top the list of almost all coastal clean-up surveys. The issue of litter is not just a visual one, the toxins adsorbed by used cigarette filters have been found to leach into the environment, and present a potential biohazard.
A range of approaches to the preparation of biodegradable filter tow have been suggested and include the use of composites of cellulose acetate with other biodegradable polymers, additives for increasing the rate of degradation of cellulose acetate, cellulose acetate with a low degree of substitution (DS) for increased biodegradability, and biodegradable polymers such as PHB/PVB and starches as the filter tow raw material.
However, to date no satisfactory commercial solution has been found for producing consumer-acceptable filters that degrade sufficiently quickly to overcome the issue of litter. One main restriction to the above approaches has been achieving an acceptable compromise between the rate of biodegradability that can be achieved and the absorption profile/taste signature given by the filter material.